The present invention relates to an installation for positioning edge to edge and welding by means of a laser beam at least two sheet blanks.
The welding by means of a laser beam of at least two sheet blanks has opened up considerable industrial possibilities, in particular in the production of butt-welded parts, for example for the automobile industry.
Indeed, sheet blanks with a butt joint therebetween, i.e. assembled edge to edge without overlapping, and welded by means of a laser beam retain all their press-forming capability.
The sheet blanks may be of different geometrical shapes and/or of different thicknesses and may even be of different grades of steel.
In order to achieve a correct butt welding by means of a laser beam of two sheet blanks so that the press-forming capacity of the welded sheet blanks remains optimum, the sheet blanks to be welded must be disposed with their edges butting against each other without gaps and, in the case of sheet blanks of different shapes, their longitudinal positioning with respect to one another must be perfect.
Further, it is essential to ensure, on one hand, a perfect lateral positioning of the sheet blanks so that the joint plane of the two sheet blanks is located on the axis of the laser beam and, on the other hand, a longitudinal and lateral relative positioning or registering of said sheet blanks during their feed so as to maintain the joint plane on the axis of the laser beam.
Further, the butt welding of at least two sheet blanks by means of a laser beam must satisfy very strict requirements of precision, shape and position of said sheet blanks to be welded.
Indeed, the quality of the weld joint partly depends on the precision in the position of the sheet blanks and in the quality of contact in the region of the joint plane between said sheet blanks.
If the quality of the contact in the region of the joint plane is incorrect, i.e. if the clearance is excessive, the welded joint presents a collapse, and even holes, and the welded joint is discontinuous in this case.
In order to ensure a minimum clearance in the region of the joint plane of the sheet blanks so as to obtain a good quality of the welded joint, it is possible to improve the quality of the shearing of the sheets and thereby limit the undulations of the cutting edges and ensure an improved contact between the sheet blanks and better control this clearance between said sheet blanks.
However, to obtain such a result, it is necessary to invest in highly expensive and very precise shearing machines or to employ double shearing machines which permit simultaneously shearing with the same blade the two sheet blanks to be butt joined.
It is also possible to exert a lateral pressure on the sheet blanks in the direction toward the joint plane of said sheet blanks so as to crush the crests of the undulations of the sheared edges to be welded.
The latter solution is employed increasingly in industrial installations for welding by means of a laser beam.
For this purpose, industrial installations, termed continuous installations, are known which permit the reception of sheet blanks, the positioning of said sheet blanks with respect to each other and with respect to the axis of the laser beam during their feed in the direction toward said laser beam, then which permit maintaining this registering sheet blank position during their travel and ensure the welding of the sheet blanks and their discharge.
In the event that it is necessary to have a different lateral pressure in accordance with the point at which said pressure is exerted, for example in the case of butt joined sheet blanks having hollows or notches or in the case where two sheet blanks having a thickness or type which is different from a third sheet blank are butt joined, the use of a continuous installation is delicate, since it is then necessary to control the pressurization of each pressure applying element in accordance with the position of the sheet blanks in the installation.
Such an operation requires a very precise control and a complicated operation.
For carrying out such welding operations industrial installations, termed static installations, are known in which the butt joined sheet blanks are fixed and the welding unit is movable along the joint plane of said sheet blanks to be welded.
Generally, these installations comprise devices for maintaining the sheet blanks which employ for each sheet blank vertical clamping systems constituted for example by clamping jaws in one unit.
But these clamping systems have the drawback of deteriorating the surfaces of the sheet blanks and exerting a uniform pressure on said sheet blanks.
Thus, in the case of the welding of a plurality of sheet blanks of different thicknesses, as the pressure exerted by the clamping systems is uniform, the quality of the welded joint is usually poor.
Further, these clamping systems do not include means for regulating the pressure as a function of the length to be welded so that it is not possible to apply the desired pressure.